Kent Park Lake Restoration
Posted:8/28/2017
Johnson
Background
Kent Park Lake is a 27 acre man-made lake in Johnson County that serves as a popular recreation destination for the surrounding communities. The lake has a 25 to one watershed to lake area ratio, and much of the land in the watershed is forested or grassland. The park is currently operated and maintained by the Johnson County Conservation Board (JCCB). Visitation at Kent Park Lake is in the top 25% of lakes statewide, and 2/3 of the watershed is in public ownership, including a number of remnant prairies within the county park.
Over the years, water quality at Kent Park Lake has degraded due to increased nutrient and sediment inputs from the watershed. Excess nutrients, especially phosphorus, have led to frequent algae blooms and low water clarity at the lake. Sedimentation in the lake has also decreased the overall lake volume and contributed to other water quality problems. Elevated bacteria levels in the lake have also resulted in swimming advisories at the beach. Kent Park Lake is considered impaired by the Iowa DNR and EPA. Research conducted by the Iowa DNR and other project stakeholders have shown that phosphorous levels in the lake must be reduced by 54% to meet state water quality standards. A combination of restoration practices will be necessary to reach water quality targets. A water quality management plan was completed in 2015 for Kent Park Lake. This project includes many efforts to meet the nutrient and sediment reduction goals identified in the plan and improve water quality in the lake.
Restoring the Lake and Park Land
In early 2016, Johnson CCB hired Stanley Engineering to design and oversee construction for in-park improvements that would help protect the lake. Stanley completed engineering design to renovate existing sediment basins in the park and build new structures that will capture nutrient and sediment run-off from entering the lake (see picture below). Costs for engineering work were split 50/50 between the Johnson CCB and the DNR Lake Restoration Program. Engineering costs were estimated at $500,000 and construction costs for the first phase of work completed in the park (watershed) were estimated at $1.2 million. Construction for watershed work started in the spring of 2017.
In addition to watershed improvements, partners are looking ahead to in-lake restoration activities. In-lake work will include some targeted dredging to re-establish depth in areas of the lake affected by sedimentation. In addition, improvements to the fishery are anticipated, with the installation of additional fish habitat and shoreline stabilization projects to provide refuge and spawning areas for sport fish. Finally, as a part of this project, the outlet structure for the lake is being assessed so that infrastructure upgrades can be made, if necessary, during the in-lake phase of this project.
In the late spring of 2017, Johnson County began drawing down Kent Park Lake so that engineering design for in-lake work could be completed and so the lake bed could de-water in advance of dredging.
In-lake work is slated to begin in the late fall or winter and will continue through 2018. Phase 2 of the project (in-lake work) is estimated to cost about $1.5 million, with a 50/50 cost share between the DNR and local funds.
When the project is completed, water clarity is expected to improve at Kent Park Lake, with the goal of reducing the frequency and intensity of blue-green algae blooms. The fishery will be re-established as soon as the lake fills, with catchable sized sport fish usually available within 3 years of the completed restoration project. This project will also help protect the longevity of Kent Park Lake, as structures placed in the watershed will slow sedimentation to the lake and infrastructure improvements to the dam and watershed catch basins will keep the lake in good shape for years to come.
